The chemical properties of organic matter affect important soil processes such as speciation, solubilization, and transport of plant nutrients and metals. This work uses ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to determine the molecular composition of three organic matter fractions of soils and aqueous extracts of crop biomass. Comparison of the van Krevelen plots allowed tracking the changes in organic matter with increasing humification. Aqueous plant biomass extracts contain a diverse mixture of lipids, proteins, and lignins. Soil aqueous extracts were marked by increases in lignin and carbohydrate components and decrease in the protein component as compared to the plant extract. Refractory humic acid fractions were marked by decrease in the lignin component and increases in the lipid and condensed aromatic components. The multivariate indicator species analysis was used to identify marker components of the four organic matter types investigated. The plant extract group had 772 marker components compared to 237 for soil aqueous extract, 92 for mobile humic acid, and 418 for calcium humic acid. This study demonstrates that ultrahigh resolution mass spectrometry and multivariate methods can be used to identify marker components to gain a molecular-scale description and understanding of C dynamics.

Information on the forms of P present in animal manure may improve our ability to manage manure P. In most investigations of manure P composition, only inorganic and total P are determined, and the difference between them is assigned as organic P. In this study, we explored the possibility of identifying and quantifying more specific organic P forms in animal manure with orthophosphate-releasing enzymes. Pig (Sus scrofa) manure and cattle (Bos taurus) manure were first sequentially fractionated into water-soluble P, NaHCO3-soluble P, NaOH-soluble P, HCl-soluble P, and residual P. The fractions were separately incubated with wheat phytase, alkaline phosphatase, nuclease P1, nucleotide pyrophosphatase, or their combinations. The released orthophosphate was determined by a molybdate blue method. Part of the organic P in those fractions could be identified by the enzymatic treatments as phytate (i.e., 39% for pig manure and 17% for cattle manure in water-soluble organic P), simple phosphomonoesters (i.e., 43% for pig manure and 15% for cattle manure in NaOH-soluble organic P), nucleotide-like phosphodiesters (2-12%), and nucleotide pyrophosphate (0-4%). Our data indicate that the enzymatic treatment is an effective approach to identify and quantify the organic P forms present in animal manures.

Organic phosphorus (Po) exists in many chemical forms that differ in their susceptibility to hydrolysis and, therefore, bioavailability to plants and microorganisms. Identification and quantification of these forms may significantly contribute to effective agricultural P management. Phosphatases catalyze reactions that release orthophosphate (Pi) from Po compounds. Alkaline phosphatase in tris-HCl buffer (pH 9.0), wheat (Triticum aestivum L.) phytase in potassium acetate buffer (pH 5.0), and nuclease P1 in potassium acetate buffer (pH 5.0) can be used to classify and quantify Po in animal manure. Background error associated with different pH and buffer systems is observed. In this study, we improved the enzymatic hydrolysis approach and tested its applicability for investigating Po in soils, recognizing that soil and manure differ in numerous physicochemical properties. We applied (i) acid phosphatase from potato (Solanum tuberosum L.), (ii) acid phosphatases from both potato and wheat germ, and (iii) both enzymes plus nuclease P1 to identify and quantify simple labile monoester P, phytate (myo-inositol hexakis phosphate)-like P, and DNA-like P, respectively, in a single pH/buffer system (100 mM sodium acetate, pH 5.0). This hydrolysis procedure released Po in sequentially extracted H2O, NaHCO3, and NaOH fractions of swine (Sus scrofa) manure, and of three sandy loam soils. Further refinement of the approach may provide a universal tool for evaluating hydrolyzable Po from a wide range of sources.

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The chemical composition of manure P is a key factor determining its potential bioavailability and susceptibility to runoff. The distribution of P forms in 13 dairy manures was investigated with sequential fractionation coupled with orthophosphate-releasing enzymatic hydrolysis. Among the 13 dairy manures, manure total P varied between 4100 and 18,300 mg kg(-1) dry matter (DM). Water-extractable P was the largest fraction, with inorganic phosphorus (P(i)) accounting for 12 to 44% of manure total P (1400-6800 mg kg(-1)) and organic phosphorus (P(o)) for 2 to 23% (130-1660 mg kg(-1)), respectively. In the NaHCO(3) fraction, P(i) varied between 740 and 4200 mg P kg(-1) DM (4-44% of total manure P), and P(o) varied between 340 and 1550 mg P kg(-1) DM (2-27% of total manure P). In the NaOH fraction, P(i) fluctuated around 200 mg P kg(-1) DM, and P(o) ranged from 130 to 630 mg P kg(-1) DM. Of the enzymatically hydrolyzable P(o) in the three fractions, phytate-like P dominated, measuring 26 to 605 mg kg(-1) DM, whereas monoester P and DNA-like P were relatively low and less variable. Although concentrations of various P forms varied considerably, significant correlations between manure total P and certain P forms were observed. For example, H(2)O-extracted P(i) was correlated with total manure P (R(2) = 0.62), and so was NaOH-extracted P(o) (R(2) = 0.81). Data also show that the amount of P released by a single extraction with sodium acetate (100 mM, pH 5.0) was equivalent to the sum of P in all three fractions (H(2)O-, NaHCO(3)-, and NaOH-extractable P). Thus, a single extraction by sodium acetate buffer could provide an efficient evaluation of plant-available P in animal manure, while the sequential fractionation approach provides more detailed characterization of manure P.

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In the ascorbic acid‐molybdenum blue method for measurement of soluble P, the relationship between color intensity and P concentration in solution and color stability is greatly affected by organic and inorganic ligands such as oxalate, citrate, tartrate, or F. The objective of this study was to evaluate the effect of these ligands and to optimize the conditions for determination of inorganic P in the presence of the interfering ligand. The critical concentrations of the ligand at which P recovery was significantly decreased were 1.5 mM for oxalate, 3.0 mM for citrate or tartrate, and 10 mM for fluoride. The interference of the ligand with P determination was overcome by excess amounts of ammonium molybdate (AM) added before the color developing reagent (CDR). The critical molybdate/ligand molar ratios (excluding the amount of molybdate added in the CDR) required to completely eliminate the interference of the ligand were 1.12 for oxalate, 0.84 for citrate, 0.56 for fluoride, and 0.34 for tartrate. The presence of ligand and excess amount of AM did not affect the linearity of color intensity against P concentration but did alter the slope, suggesting that the modified method is reliable for P determination in the presence of an interfering ligand provided that the standard curve is prepared in the same matrix as the sample.